This invention relates in general to fluorescence polarization immunoassays (FPIA) and modifications of current processes for detection of several commonly abused drugs in biological fluid wherein sequential or simultaneous performance of more than one FPIA assay is achieved utilizing a single cuvette. Combination of FPIA reagents and manual or software technologies allows for performance of at least two FPIA assays per cuvette. In another aspect, the invention relates to combination FPIA on analytes other than abused drugs.